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Old 25-09-2020, 07:56   #1
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Dyneema schackles

Hi everyone..So here is my brilliant idea for securing my boat for potentially the entire winter:

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5 Ton displacement..self made dyneema shackles. We have Sirocco winds heading this way tomorrow (30kts expected)..I shall report
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Old 25-09-2020, 08:13   #2
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Re: Dyneema schackles

Quote:
Originally Posted by crankysailor View Post
Hi everyone..So here is my brilliant idea for securing my boat for potentially the entire winter:

Attachment 224165

5 Ton displacement..self made dyneema shackles. We have Sirocco winds heading this way tomorrow (30kts expected)..I shall report

I've long used loops (does not need to be a shackle in most cases) covered with webbing for chafe to save space on shared cleats. A strong loop can serve several lines.
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Old 25-09-2020, 08:17   #3
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Re: Dyneema schackles

Good luck

what's the metal piece (on the left) - is that some sort of mooring spring? Perhaps an isure?

How hard did you pre-tension up that diamond knot? Did you get it up to working load?
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Old 25-09-2020, 22:47   #4
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Re: Dyneema schackles

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Originally Posted by Breaking Waves View Post
Good luck

what's the metal piece (on the left) - is that some sort of mooring spring? Perhaps an isure?

How hard did you pre-tension up that diamond knot? Did you get it up to working load?


A mooring spring, yes.. used commonly around here. The ring is polished so I wouldn't expect any abrasion. The clamp itself is fairly smooth though not polished.

Regarding pre tension.. well I have heard of folks using winches but I wasn't on the boat when I made them. I basically hung on them with my body weight. Now that you mention it that feels kind of silly but I reasoned it wouldn't be orders of magnitude away from what a winch would pull ... or would it?
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Old 26-09-2020, 05:25   #5
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Re: Dyneema schackles

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Originally Posted by crankysailor View Post
A mooring spring, yes.. used commonly around here. The ring is polished so I wouldn't expect any abrasion. The clamp itself is fairly smooth though not polished.

Regarding pre tension.. well I have heard of folks using winches but I wasn't on the boat when I made them. I basically hung on them with my body weight. Now that you mention it that feels kind of silly but I reasoned it wouldn't be orders of magnitude away from what a winch would pull ... or would it?
It depends on your displacement.
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Old 26-09-2020, 05:57   #6
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Re: Dyneema schackles

As an alternative that is stronger and easy to move, consider splicing a loop and then tying a prusik on the post of your cleat.
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Old 26-09-2020, 06:09   #7
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Re: Dyneema schackles

My preference is an endless loop cow-hitched to the mooring line then the other end of the loop put through the center opening of the cleat, then wrapped back up and over the ears of the cleat.
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Old 26-09-2020, 06:25   #8
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Re: Dyneema schackles

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My preference is an endless loop cow-hitched to the mooring line then the other end of the loop put through the center opening of the cleat, then wrapped back up and over the ears of the cleat.

This.


I have also cow hitched one around two mooring lines, as though making a JSD bridle, and then gone to the cleat. I do this when there are too few or too small cleats.


In this case, I might cover it with webbing because I'm worried about the Dyneema overloading the nylon (small diameter).
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Old 26-09-2020, 06:51   #9
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Re: Dyneema schackles

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Originally Posted by crankysailor View Post
Regarding pre tension.. well I have heard of folks using winches but I wasn't on the boat when I made them. I basically hung on them with my body weight. Now that you mention it that feels kind of silly but I reasoned it wouldn't be orders of magnitude away from what a winch would pull ... or would it?

Yea, actually probably quite near an order of magnitude . . .150-200lbs vs 2000-3500lbs.

You really really should not cut the tails short until they are loaded up near to working strength. A diamond, which has not been properly pre-tensioned will slip/compress some quite good distance when the load comes on and will suck those short tails into the knot and come untied. We had a (offroad recovery) video showing exactly this here quite recently in another thread.

If you can't or don't want to preload that high, you should just simply leave the tails long (like 4"-6" sticking out of the knot) until they get worked up to near working load (like thru a 35 kt blow). It's not quite as nice looking with long tails but it is not horrible and there is pretty much no functional problem with it.

This is not an idle problem . . . it is the most common failure point of diamond soft shackles - even from 'pro' constructed ones I have tested . . . people just don't tension them enough and then cut the tails super short, and they then suck the tail in and come untied way way short of the strength they should/could have.

Back when we were developping/refining soft shackles on that old sailing anarchy thread . . . there was a debate about what strength we should cite for them. I argued we should cite the strength of a 'well made one'. While another participant said we should cite the strength of 'a typical diy job'. And the difference is very roughly double.
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Old 26-09-2020, 09:26   #10
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Re: Dyneema schackles

Instead of the diamond knot, I recommend to use the Brian Toss (button) knot
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Old 26-09-2020, 10:00   #11
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Re: Dyneema schackles

I only use shackles where I want to open / close frequently.


In the application as pictured I use closed loops.


I do so because I had a shackle open on me one time. I can't say why - it was fine for 600 miles run then it opened. I must have done something wrong.



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Old 26-09-2020, 10:14   #12
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Re: Dyneema schackles

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I recommend to use the Brian Toss (button) knot
yes, it is preferred for a number of reasons . . . . it is not as widely known and is more difficult to learn (easy once you learn it, but harder for people to pick up). For the vast majority of applications, both/either work fine if done correctly with care.
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Old 26-09-2020, 11:08   #13
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Re: Dyneema schackles

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Originally Posted by crankysailor View Post
A mooring spring, yes.. used commonly around here. The ring is polished so I wouldn't expect any abrasion. The clamp itself is fairly smooth though not polished.

Regarding pre tension.. well I have heard of folks using winches but I wasn't on the boat when I made them. I basically hung on them with my body weight. Now that you mention it that feels kind of silly but I reasoned it wouldn't be orders of magnitude away from what a winch would pull ... or would it?
I think it WOULD be orders of magnitude. That is a winch could easily pull 5-10 times your body wt. However, button knot isn’t going to come undone it may distort some and look weird.
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Old 26-09-2020, 18:00   #14
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Re: Dyneema schackles

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I think it WOULD be orders of magnitude. That is a winch could easily pull 5-10 times your body wt.
Actually, that is (at 10 times body weight) only one order of magnitude, not "orders of magnitude". At 5 times body weight, less than a single order of magnitude.

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Old 27-09-2020, 08:23   #15
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Re: Dyneema schackles

Quote:
Originally Posted by crankysailor View Post
Hi everyone..So here is my brilliant idea for securing my boat for potentially the entire winter:

Attachment 224165

5 Ton displacement..self made dyneema shackles. We have Sirocco winds heading this way tomorrow (30kts expected)..I shall report


We have been using this method for a number of years after destroying our dock lines from cleat chafe. Stacking a number of lines over each other(no choice) and a enough swell to break some of the floating docks did the job. BTW all with firehose.

We make the dynema soft shackles a bit longer and run it thru a piece of fire hose. We tie our nylon dock lines onto the soft shackle. We can get 3 dock lines on one clear without any issue.

Since we switched to this method no issues with chafe
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